The bowl is always black , stays clean a day, and its deity when it gets flushed. Why

How many bathrooms and kitchens drain into it, including all floors above?
Does anyone use it?
Sounds like it isn't draining all the way because of sewage backing up!

Also, does the toilet tank need cleaning?

1- kitchen sink, 1- bathroom sink and tiolet bowl. Yes it is being used. What can I do about it.

No,my daughter cleans often becaude its discusting

y daugNo mhter cleans all the time, its so discusting

1- kitchen sink, 1- bathroom sink and tiolet bowl. Yes it is being used. What can I do about it.

No,my daughter cleans often becaude its discusting

y daugNo mhter cleans all the time, its so discusting
INSIDE the toilet tank, too?

The answer is probably going to depend on what the plumbing looks like under the basement floor, IF it is under it. Sometimes it goes up before it goes out to the city sewer.
Toilets are designed to act as a 'trap' so that sewer gas can't escape, but it doesn't mean that waste water from plumbing above (toilets, but also kitchen sinks) doesn't mix backwards towards your toilet.
You really need a plumber who has a camera on a snake. You should watch it with him.
It could be an easy fix, or an expensive one.
If the drain is old enough, it could mean removing concrete and replumbing it.
Talk to the plumber about options. One might be building steps up to a toilet about a foot or more above the floor. Not so terrible, and might be the cheapest.

Assuming your toilet drains by gravity ( no sewer ejector )...

Looks you need to snake your main line. When you flush above, water drops down, passea by basement toilet, hits sludge inside the main sewer and bounces back, into the basement toilet. What you see is the residue of sludge.

Call Roto Rooter service, have them to dismount that basement toilet and snake the main through toilet hole in the floor, as far as the can

Hope that helps

Milo